Researchers demonstrate gravitational instability in granular materials for the first time

rayleigh taylor instability
A numerical simulation of Rayleigh Taylor instability with the help of fluid dynamics code. ( Credits - Vimeo)

Natural phenomenon such as volcanoes and mudslides can be explained by the movement of granular particles like sand. This time engineers illustrated how bubbles are formed in the sand of lighter grain as same as other liquids even though powder materials move towards each other when mixed. Though grains present in the sand are solid when the huge volume is mixed it behaves like a liquid. Falling sand dunes or sand flowing through an hourglass are known as granular materials and the science of how they flow is still unknown.

Rayleigh-Taylor instability a mechanism in fluid dynamics explains the reason that it happens between two fluids having different densities and the light fluid thrusts the heavy fluids just like oil comes up when mixed with water. Engineers of Columbia University and ETH Zurich had discovered something likely. Chris Boyce of Columbia University, a chemical engineer said that they think their discovery can be transformed. The group discovered that upwards gas flow between granular material and vibration both produces a process alike RT instability. The study has been published in the Proceedings of the National Academy of Sciences In this process, the lighter grain starts to move upwards in between heavier grains forming fingers and bubbles. 

This works just like oil and water but they never mix whereas sand mixes. The bubbles are formed because the group of lighter grain allows the gas to flow through it easier than the heavier grains which rise the tension of the upward drag force and downward contact forces created by gas flow which creates RT instability making the results similar to that of RT instabilities in liquid but the process is different.

The researchers also noticed captivating things like the cascade branch of a descending granular droplet as mentioned in their paper. The weight of the droplets moving downwards of the heavier grains create a chain of force downwards thus not letting the drops to pass through. So the droplets break into branches while moving downwards creating somewhat similar to lightning. Another discovery was the instability similar to RT can occur when there is a huge range of flow of gas and conditions of vibration which can be used as a help in understanding the role of subterranean processes at the time of earth tremors.

Boyce said that their discovery can not only be used to describe the process of the formation of mineral deposits and geological formations but also in technologies of powder-processing in the energy, pharmaceuticals industries, and constructions. Thus we can conclude that the study of bubbles is helping to find out new things behind geological factors.


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